The present invention relates to a video tape recorder (VTR) for recording and reproducing video signals and, more specifically, to a digital/analog compatible VTR which is capable of dealing with both digital and analog video signals.
Current domestic VTRs are analog VTRs using 1/2 in. oxide tapes for recording analog TV signals.
Digital broadcasting systems have been developed as TV broadcasting systems of the next generation and efforts have been made for the development of practical transmission systems, for digital transmission using satellites, ground waves and cables. For example, there is in the U.S.A. an ATV (Advanced Television) system using a bandwidth of 6 MHz, which is used for current TV broadcasting, that processes wide-band video signals of high definition (hereinafter referred to as "High Definition (HD) video signals") higher than those of video signals of the current NTSC system and the PAL system (hereinafter referred to as "Standard Definition (SD) video signals) into compressed and coded digital video signals. The MPEG (Moving Picture Experts Group) system is a known SD video signal system. Refer to Terebijon Gakkai-shi, Vol. 47, No. 4, pp. 486-503 (1993) for the further details concerning digital broadcasting systems.
It is expected that those digital broadcasting systems will be employed together with analog TV broadcasting systems in the near future. Accordingly, for practical use of digital broadcasting or digital transmission, a practical development is expected to be made of VTRs of the digital recording system type which are capable of recording digital signals utilizing the feature of digital transmission in which signals are not deteriorated by transmission systems. However, digital VTRs have been used practically only in special fields, such as in the business field because the information content of digital video signals is greater than that of analog video signals. Recent advancement in image-compressing techniques represented by the MPEG system has made possible the miniaturization of digital equipments and the extended use of digital techniques for domestic equipments. Refer to Terebijon Gakkai-shi, Vol. 47, No. 6, pp. 814-825 (1993) for further details concerning digital recording techniques. Domestic digital VTRs having an original recording format have been developed. However, most users keep analog-recorded tapes collected as property, and there are problems in digital VTRs in price, floor space necessary for installation and the use of the collected analog-recorded tapes.
Accordingly, VTRs capable of recording and reproducing signals in both the analog system and the digital system have been desired. However, it is expected that the following problems reside in VTRs capable of dealing with both analog and digital systems. Firstly, since analog recording and digital recording use different input sources, respectively, the user needs to select the recording system and the input source and to confirm the coincidence of the selected recording system and input source, which requires troublesome operations for recording and increases the possibility of erroneous operations. Secondly, there are problems in using tape cassettes of the same shape, including those containing tapes on which signals are recorded by the analog system and those on which signals are recorded by the digital system. For example, when recording signals on a tape carrying recorded signals by the current analog VTR in a continuous mode or an overwrite mode, the contents of the tape must be reproduced tentatively for confirmation. However, when tapes of both the analog system and the digital system are used together, the user is unable to recognize pictures recorded by either system unless the reproducing system coincides with the selected recording system and the input source; consequently, there is the possibility that the user misunderstands that no signal is recorded on the tape and overwrites new signals on the tape, thereby erasing the previously-recorded signal mistakenly. In addition, when an increasing number of recorded tapes of the digital system are used, there is a problem that the user is unable to recognize signals recorded on the tape of the digital system with the current analog VTRs, resulting in erasing of the previously-recorded signal mistakenly.
Most current analog VTRs are provided with an audio head independently of a video head on a rotary drum to record FM signals in the depth of a magnetic tape. Therefore, it is disadvantageous from the point of view of cost and productivity to provide on a rotary drum a magnetic head specially for digital recording and reproducing and a proposal is made for the use of an audio head also for digital recording. However, when an FM audio head is used also as a digital head, an audio signal processing circuit is actuated, which processes digital signals for audio processing when reproducing the digital signals and supplies the audio-processed digital signals to a loudspeaker. Then, the loudspeaker generates abnormal sounds and, in the worst case, the loudspeaker might be destroyed. Although the conventional VTR has an automatic tracking control function to provide reproduced outputs on the highest level, the VTR needs a new automatic tracking control function for operation in a digital recording mode. When the VTR is provided with a decoding circuit for expanding compressed and coded digital video signals and converting the expanded digital video signals into composite video signals, the circuits need to be changed according to mode identifying information.